1. Field of the Invention
The present invention relates to an apparatus for converting light energy into electric energy and storing the same. In particular, it relates to an energy system in which a photoelectric conversion unit which utilizes a bulk photovoltaic effect and a unit for storing electric energy generated by the unit are combined.
2. Description of the Related Art
In the prior art, an energy converting apparatus for converting light energy into electric energy has been known as a solar battery comprising a semiconductor such as Si, GaAs or the like having a p-n junction. Further, there has been known an energy system in which converted electric energy is stored in a secondary battery so as to make it possible to output the converted energy at a desired time.
When light is irradiated onto the semiconductor having the p-n junction, electrons and positive holes generated by the light irradiation at the junction portion diffuse toward the n and p type sides respectively, and a voltage depending upon the energy band gap (about 0.5 V) is obtained. Due to this low voltage, in the system in which the solar battery utilizing the semiconductor and the secondary battery are combined, a required voltage has been obtained in practical use by connecting a large number of secondary batteries with semiconductor elements in series, or by connecting a booster unit with the secondary battery.
However, there have been such problems that when the secondary batteries are connected in series, the internal resistance increases depending on the number of connected batteries to make the loss of energy large, while when the booster unit is used, the unit requires driving energy therefor. Further, the solar battery has a drawback such that the generating efficiency lowers in accordance with an increase in temperature, resulting in inferior reliability.